1. Field of the Invention
The invention relates generally to surgically implantable flow restrictors, and more particularly to a cuff that is attachable directly to a tubular organ for increasing the flow resistance of liquids and substances through the tubular organ.
2. Discussion of the Prior Art
Biological tubular organs in our body are conduits for fluids, food and wastes. For example, the urethra is the conduit for urine between the bladder and the urethral meatus and it also functions to inhibit involuntary leakage. In stress urinary incontinence, urine leaks involuntarily when the person coughs or laughs.
Stress urinary incontinence occurs most commonly in women and is managed by absorbents and by surgical interventions. Many surgeries involve the implantation of a medical device to help decrease incontinence for the patient. Among these implantable medical devices for women, urethral slings, in the form of a strip of material or tissue to support under the bladder neck or mid-urethra, and with its ends anchored in anatomical locations other than the urethra or bladder, such as the pubic synthesis, and the abdominal muscles. Such slings have been favored by many urologists and gynecologists. The sling acts as a hammock to support and to lift the sagging urethra and/or bladder neck back to a normal position. This stops the bladder neck or urethra from dropping during sudden movements to minimize urine leakage. The newer generation of slings generally is implanted in one of three approaches. It is approached from the below, Ulmsten, U.S. Pat. No. 6,491,703 (the vaginal approach); from on top, Staskin et al. U.S. Pat. No. 6,612,977 (the suprapubic approach); and from below and goes laterally to the two sides (the transobturator approach, Monarc Subfascial Hammock from American Medical Systems). All three approaches involve the use of long rods passing blindly from one anatomical site to the other, and often resulting in puncturing of the bladder and/or blood vessels. Though the transobturator approach avoids the retropubic space and does not lead to puncturing of the bladder, it suffers as the other two in that it involves anatomical structures outside of the urinary tract system and thus, typically, not familiar to urological surgeons. In addition, a precise adjustment of the sling tension for each patient is not possible. This ill adjustment results in lower than expected level of efficacy and complications including urethral erosions. Furthermore, as the sling is being anchored in anatomical structures other than the urethra, it presents complications, such as injuries to bladder, blood vessels, nerves and muscles and is contraindicated for women patients who intend to have child births in the future.
For extreme cases, an artificial urinary sphincter (AUS) is implanted for the incontinence where a band, similar to a blood-pressure cuff, fully surrounds the urethra. Fluid is made to enter the band and constantly exerts compression to the urethra to occlude the urethral lumen. The patient needs to actively pump the fluid out of the band and into a balloon reservoir implanted in the abdominal area every time the patient needs to void. The AUS is a complex system and the associated surgical procedure is major, complex and long. Buuck, in U.S. Pat. No. 3,863,622 (1975), Burton, in U.S. Pat. No. 4,222,377 (1980) and Polyak, in U.S. Pat. No. 4,994,020 (1991) described an artificial sphincter (AUS) system that is a totally occlusive device having an inflatable band completely surrounding the patient's urethra. The urethra is essentially occluded continuously and constantly until the fluid in the band is actively pumped out by the patient at the time when he or she desires to urinate. Once the fluid is pumped out the AUS band, the compression surrounding the urethra is diminished and the urethral lumen for passage of urine can then open. With the AUS, patients cannot urinate without first having to actively manipulate the device to pump the fluid out of the band and into a reservoir at a distant location to remove the urethral occlusion.
Urethra is only one of the many biological tubes in the body. Other biological tubular organs include the esophagus, stomach, colon, blood vessels and the heart. All these tubes can suffer from defects and lose their intended function in controlling flow of material and fluids within them.
Broadly speaking, the present invention comprises a cuff that only partially surrounds an anatomical tubular organ, such as the urethra. Many biological soft tissue tubes are expandable in girth to accommodate passage of material through their lumen. The muscle components in the wall of the tube provide tonicity and elasticity. For example, the stomach expands as food enters, the esophagus opens up to allow food to pass down, the lower esophageal sphincter or the cardiac sphincter opens to allow passage of food but closes to prevent regurgitation of food material and stomach acid up the esophagus, intestines expand to accommodate food material and provides peristaltic action to propagate the food material down its length, and the urethra expands to allow urine to flow through. After the material has exited, the diameter of the tubular organ again retracts to its non-expanded size. The attachment of a partial cuff, made of non-elastic or limited elasticity material, and that only partially surrounds the tubular organ, will limit the expansion of the portion of the tubular organ covered by the cuff, allowing only the non-covered portion to expand. For material to pass through this juncture with the reduced expandable wall tissue, a higher force is required to open the passage way. The reduced amount of expandable tissue at the site of the partial cuff results in a higher tissue tension that would require a higher force in order to push the same amount of material through this juncture. If the cuff has been made to completely surround the tubular organ with a closed lumen, then little or no material will be able to pass through this juncture. However, when the cuff only partially surrounds the tubular organ, the portion that is not restrained by the cuff will still be able to expand, allowing passage of material. The lesser amount of tissue allowed to expand results in either a higher pressure to open the lumen to the same size or allowing only a smaller lumen to be opened due to limits on tissue stretch, or both. The partial cuff of the current invention induces an increased tonicity to the biological tubular organ. This is one of the unique and non-obvious principles of the invention, providing a means to increase material passage resistance in a biological soft tissue tube while still maintaining the profile of the biological tube.
When used in treating stress urinary incontinence, the partial cuff of the present invention does not occlude the urethra, but only add reinforcement to maintain the urethral closure pressure. Benefits of such a partial cuff include improving continence and allowing patients to void naturally and volitionally. This augmentation of a higher urethral tonicity for closure means an increased resistance to urine flow in stress situations such as when the patient laughs and coughs. As the cuff becomes an integral portion of and moves with the urethra, its ability to provide continence is not affected by the physical position the patient happens to be in or gravity. Because the partial cuff attaches to only the urethra and is not tied to other tissues and bones, the present invention also avoids many of the possible adverse events, contraindications and pitfalls with the traditional slings. As it involves only the urinary tract anatomy, urological surgeons will have intimate knowledge of the operating field and its surgical implantation will not involve long rods passing blindly through various anatomical structures.